In the mineral mining, it is well known to use chains to drive machinery. For example, it is well known to use a chain to drive a plough back and forth alongside a mineral, e.g. coal face. In such drive systems it is also known to measure load forces with strain gauges and to disconnect the drive in the event of overload. The strain gauges can be incorporated into pins or rods fitting into gearing (see DE-OS 3,323,251 and DE-OS 3,323,250).
With chain drives it is often necessary to subject the chain to a specific preliminary tension. If the tension is too low, slackness can occur which can cause interruption in operation if the chain springs off its chain wheel or whipping which is dangerous to personnel. Conversely, if the tension is set too high then the chain, the bearings and associated components will be subjected to premature wear. It is thus known to incorporate chain tension adjustement mechanisms, such as hydraulic piston and cylinder units, to displace one or both chain wheels around which the chain is entrained. Hitherto there has been no accurate means for determining the tension in the chain and there is a need for such means.